Method for triggering a sidelink buffer status reporting in a d2d communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for triggering a sidelink buffer status reporting in a D2D communication system, the method comprising: configuring a first ProSe destination including at least one first UE and a second ProSe destination including at least one second UE; receiving a first sidelink data for a first sidelink logical channel from an upper layer; receiving a second sidelink data for a second sidelink logical channel from the upper layer while the UE has the first sidelink data for the first logical channel, wherein the second logical channel has a higher priority than a priority of the first sidelink logical channel; and triggering a buffer status reporting the if the first sidelink logical channel and the second sidelink logical channel belong to a same ProSe destination.

Pursuant to 35 U.S.C. §119(e), this application claims the benefit ofU.S. Provisional Patent Application No. 62/246,618, filed on Oct. 27,2015 and U.S. Provisional Patent Application No. 62/250,525, filed onNov. 4, 2015, the contents of which are all hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method for triggering a sidelink buffer statusreporting in a D2D (Device to Device) communication system and a devicetherefor.

Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. Details ofthe technical specifications of UMTS and E-UMTS are provided in Release7 and Release 8 of “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network”, for example.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, standardinstitutes such as 3GPP or IEEE have proceeded to establish a D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that D2D communication contributes to increase throughputof a mobile communication system and create new communication services.Also, D2D communication may support proximity based social networkservices or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

D2D communication technologies such as infrared communication, ZigBee,radio frequency identification (RFID) and near field communications(NFC) based on RFID have been already used. However, since thesetechnologies support communication only of a specific object within alimited distance (about 1 m), it is difficult for the technologies to bestrictly regarded as D2D communication technologies.

Although D2D communication has been described as above, details of amethod for transmitting data from a plurality of D2D user equipmentswith the same resource have not been suggested.

SUMMARY OF THE INVENTION

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE; and

FIG. 12 is a diagram for MAC structure overview in a UE side;

FIG. 13 is an example for sidelink configurations for triggering asidelink buffer status reporting in a D2D communication system accordingto embodiments of the present invention;

FIGS. 14 and 15 are diagrams for triggering a sidelink buffer statusreporting in a D2D communication system according to embodiments of thepresent invention; and

FIG. 16 is a diagram for triggering a sidelink buffer status reportingin a D2D communication system according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described in thecontext of a long term evolution (LTE) system and a LTE-advanced (LTE-A)system in the present specification, they are purely exemplary.Therefore, the embodiments of the present invention are applicable toany other communication system corresponding to the above definition. Anexemplary system in which the invention disclosed herein may beimplemented is a system compliant with the 3GPP specification TS 36.321Version 12.6.0. In addition, although the embodiments of the presentinvention are described based on a frequency division duplex (FDD)scheme in the present specification, the embodiments of the presentinvention may be easily modified and applied to a half-duplex FDD(H-FDD) scheme or a time division duplex (TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an Si interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transciver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals).

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a Layer 2 structure forSidelink.

Sidelink communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform sidelink communication.

In order to perform synchronization for out of coverage operation UE(s)may act as a synchronization source by transmitting SBCCH and asynchronization signal. SBCCH carries the most essential systeminformation needed to receive other sidelink channels and signals. SBCCHalong with a synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH are derived from the parameters signalled by the eNB. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH is derived from the received SBCCH;otherwise UE uses pre-configured parameters. SIB18 provides the resourceinformation for synchronization signal and SBCCH transmission. There aretwo pre-configured subframes every 40 ms for out of coverage operation.UE receives synchronization signal and SBCCH in one subframe andtransmit synchronization signal and SBCCH on another subframe if UEbecomes synchronization source based on defined criterion.

UE performs sidelink communication on subframes defined over theduration of Sidelink Control period. The sidelink Control period is theperiod over which resources allocated in a cell for sidelink controlinformation and sidelink data transmissions occur. Within the sidelinkControl period the UE sends sidelink control information followed bysidelink data. sidelink control information indicates a Layer 1 ID andcharacteristics of the transmissions (e.g. MCS, location of theresource(s) over the duration of Sidelink Control period, timingalignment).

The UE performs transmission and reception over Uu and PC5 with thefollowing decreasing priority order:

-   -   Uu transmission/reception (highest priority);    -   PC5 sidelink communication transmission/reception;    -   PC5 sidelink discovery announcement/monitoring (lowest        priority).

FIG. 10A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10B is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 10A shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 10A.

User plane details of ProSe Direct Communication: i) there is no HARQfeedback for sidelink communication, ii) RLC UM is used for sidelinkcommunication, iii) RLC UM is used for sidelink communication, iv) areceiving RLC UM entity used for sidelink communication does not need tobe configured prior to reception of the first RLC UMD PDU, and v) ROHCUnidirectional Mode is used for header compression in PDCP for sidelinkcommunication.

A UE may establish multiple logical channels. LCID included within theMAC subheader uniquely identifies a logical channel within the scope ofone Source Layer-2 ID and ProSe Layer-2 Group ID combination. Parametersfor logical channel prioritization are not configured. The Accessstratum (AS) is provided with the PPPP of protocol data unit transmittedover PC5 interface by higher layer. There is a PPPP associated with eachlogical channel.

SL-RNTI is an unique identification used for ProSe Direct CommunicationScheduling.

The Source Layer-2 ID identifies the sender of the data in sidelinkcommunication. The Source Layer-2 ID is 24 bits long and is usedtogether with Destination Layer-2 ID and LCID for identification of theRLC UM entity and PDCP entity in the receiver.

The destination Layer-2 ID identifies the target of the data in sidelinkcommunication. The Destination Layer-2 ID is 24 bits long and is splitin the MAC layer into two bit strings: i) One bit string is the LSB part(8 bits) of Destination Layer-2 ID and forwarded to physical layer asGroup Destination ID. This identifies the target of the intended data insidelink control information and is used for filtering of packets at thephysical layer. And ii) Second bit string is the MSB part (16 bits) ofthe Destination Layer-2 ID and is carried within the MAC header. This isused for filtering of packets at the MAC layer.

No Access Stratum signalling is required for group formation and toconfigure Source Layer-2 ID, Destination Layer-2 ID and GroupDestination ID in the UE. These identities are either provided by higherlayer or derived from identities provided by higher layer. In case ofgroupcast and broadcast, the ProSe UE ID provided by higher layer isused directly as the Source Layer-2 ID and the ProSe Layer-2 Group IDprovided by higher layer is used directly as the Destination Layer-2 IDin the MAC layer. In case of one-to-one communications, higher layerprovides Source Layer-2 ID and Destination Layer-2 ID.

FIG. 10B shows the protocol stack for the control plane.

A UE does not establish and maintain a logical connection to receivingUEs prior to one-to-many a sidelink communication. Higher layerestablish and maintain a logical connection for one-to-one sidelinkcommunication including ProSe UE-to-Network Relay operation.

The Access Stratum protocol stack for SBCCH in the PC5 interfaceconsists of RRC, RLC, MAC and PHY as shown below in FIG. 10B.

The PPPP is a ProSe Per-Packet Priority. The ProSe Per-Packet Priorityis summarized as follows:

i) a single UE shall be able to transmit packets of different prioritieson PC5, ii) the UE upper layers provide to the access stratum a ProSePer Packet Priority from a range of possible values, iii) the ProSe PerPacket Priority is used to support preferential transmission of packetsboth intra-UE and across different UEs, iv) the support of 8 prioritylevels for the ProSe Per Packet Priority should be sufficient, v) theProSe Per Packet Priority applies to all PC5 traffic, and vi) the ProSePer Packet Priority is independent of the layer-2 destination of thetransmission.

From the above summary, it seems that SA2 think ProSe packetprioritization based on PPP is very important and should be supported inPC5 interface in any case. Keeping this observation in mind, we explainhow the LCP procedures should be changed from Rel-12.

FIG. 11 is an example for PC5 interface between remote UEs and a relayUE.

In ProSe, a UE communicates with other UEs directly over PC5 interface.

By introducing a Relay UE for UE-to-NW relay, a remote UE transmits datato an eNB via the Relay UE, and the eNB transmits data to the remote UEvia the Relay UE. I.e., the Relay UE relays data to/from eNB.

As data transfer between the remote UE and the Relay UE is ProSecommunication, the Relay UE is communicating with the remote UE over PC5interface. In the meantime, as data transfer between the Relay UE andthe eNB is a normal uplink/downlink (Uu) communication, the Relay UE iscommunicating with the eNB over Uu interface. This implies that if datahas higher priority in PC5 communication, it should also be higherprioritized in Uu communication.

Over PC5 interface, Per-Packet Priority (PPP), is used to prioritize acertain packet, where the priority is independent with ProSe destinationor ProSe UE. In order to prioritize the packet with higher priority overUu interface as well, the Relay UE needs to know the priority of thepacket so that the Relay UE provides more opportunities of transmissionto the packet with higher priority.

In order to transmit on the SL-SCH, the MAC entity must have a sidelinkgrant. The sidelink grant is selected as follows: if the MAC entity isconfigured to receive a sidelink grant dynamically on the PDCCH and moredata is available in STCH than can be transmitted in the current SCperiod, the MAC entity shall determine a set of subframes in whichtransmission of SCI and transmission of first transport block occurusing the received sidelink grant, consider the received sidelink grantto be a configured sidelink grant occurring in those subframes startingat the beginning of the first available SC Period which starts at least4 subframes after the subframe in which the sidelink grant was received,overwriting a previously configured sidelink grant occurring in the sameSC period, if available, and clear the configured sidelink grant at theend of the corresponding SC Period.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of SCI, the MAC entity shall, for each subframe, instructthe physical layer to transmit SCI corresponding to the configuredsidelink grant.

If the MAC entity has a configured sidelink grant occurring in thissubframe, and if the configured sidelink grant corresponds totransmission of first transport block, the MAC entity shall deliver theconfigured sidelink grant and the associated HARQ information to theSidelink HARQ Entity for this subframe.

For PDU(s) associated with one SCI, MAC shall consider only logicalchannels with same Source Layer-2 ID-Destination Layer-2 ID pairs.

FIG. 12 is a diagram for MAC structure overview in a UE side.

The MAC layer handles logical-channel multiplexing, hybrid-ARQretransmissions, and uplink and downlink scheduling. It is alsoresponsible for multiplexing/demultiplexing data across multiplecomponent carriers when carrier aggregation is used.

The MAC provides services to the RLC in the form of logical channels. Alogical channel is defined by the type of information it carries and isgenerally classified as a control channel, used for transmission ofcontrol and configuration information necessary for operating an LTEsystem, or as a traffic channel, used for the user data. The set oflogical-channel types specified for LTE includes:

The Broadcast Control Channel (BCCH), used for transmission of systeminformation from the network to all terminals in a cell. Prior toaccessing the system, a terminal needs to acquire the system informationto find out how the system is configured and, in general, how to behaveproperly within a cell.

The Paging Control Channel (PCCH), used for paging of terminals whoselocation on a cell level is not known to the network. The paging messagetherefore needs to be transmitted in multiple cells.

The Common Control Channel (CCCH), used for transmission of controlinformation in conjunction with random access.

The Dedicated Control Channel (DCCH), used for transmission of controlinformation to/from a terminal. This channel is used for individualconfiguration of terminals such as different handover messages.

The Multicast Control Channel (MCCH), used for transmission of controlinformation required for reception of the MTCH.

The Dedicated Traffic Channel (DTCH), used for transmission of user datato/from a terminal. This is the logical channel type used fortransmission of all uplink and non-MBSFN downlink user data.

The Multicast Traffic Channel (MTCH), used for downlink transmission ofMBMS services.

To support priority handling, multiple logical channels, where eachlogical channel has its own RLC entity, can be multiplexed into onetransport channel by the MAC layer. At the receiver, the MAC layerhandles the corresponding demultiplexing and forwards the RLC PDUs totheir respective RLC entity for in-sequence delivery and the otherfunctions handled by the RLC. To support the demultiplexing at thereceiver, a MAC is used. To each RLC PDU, there is an associatedsub-header in the MAC header. The sub-header contains the identity ofthe logical channel (LCID) from which the RLC PDU originated and thelength of the PDU in bytes. There is also a flag indicating whether thisis the last sub-header or not. One or several RLC PDUs, together withthe MAC header and, if necessary, padding to meet the scheduledtransport-block size, form one transport block which is forwarded to thephysical layer.

In addition to multiplexing of different logical channels, the MAC layercan also insert the so-called MAC control elements into the transportblocks to be transmitted over the transport channels. A MAC controlelement is used for inband control signaling—for example, timing-advancecommands and random-access response. Control elements are identifiedwith reserved values in the LCID field, where the LCID value indicatesthe type of control information. Furthermore, the length field in thesub-header is removed for control elements with a fixed length.

The MAC multiplexing functionality is also responsible for handling ofmultiple component carriers in the case of carrier aggregation. Thebasic principle for carrier aggregation is independent processing of thecomponent carriers in the physical layer, including control signaling,scheduling and hybrid-ARQ retransmissions, while carrier aggregation isinvisible to RLC and PDCP. Carrier aggregation is therefore mainly seenin the MAC layer, where logical channels, including any MAC controlelements, are multiplexed to form one (two in the case of spatialmultiplexing) transport block(s) per component carrier with eachcomponent carrier having its own hybrid-ARQ entity.

Meanwhile, UEs that already have a valid grant obviously do not need torequest uplink resources. However, to allow the scheduler to determinethe amount of resources to grant to each terminal in future subframes,information about the buffer situation and the power availability isuseful, as discussed above. This information is provided to thescheduler as part of the uplink transmission through MAC controlelement. The LCID field in one of the MAC subheaders is set to areserved value indicating the presence of a buffer status report.

From a scheduling perspective, buffer information for each logicalchannel is beneficial, although this could result in a significantoverhead. Logical channels are therefore grouped into logical-channelgroups and the reporting is done per group. The buffer-size field in abuffer-status report indicates the amount of data available transmissionacross all logical channels in a logical-channel group.

From a scheduling perspective, buffer information for each logicalchannel is beneficial, although this could result in a significantoverhead. Logical channels are therefore grouped into logical-channelgroups and the reporting is done per group. The buffer-size field in abuffer-status report indicates the amount of data available transmissionacross all logical channels in a logical-channel group.

The Buffer Status Reporting (BSR) procedure is used to provide a servingeNB with information about the amount of data available for transmission(DAT) in the UL buffers of the UE. RRC may control BSR reporting byconfiguring the three timers periodicBSR-Timer and retxBSR-Timer andlogicalChannelSR-ProhibitTimer and by, for each logical channel,optionally signaling Logical Channel Group (LCG) which allocates thelogical channel to an LCG

The sidelink Buffer Status reporting procedure is used to provide theserving eNB with information about the amount of sidelink data availablefor transmission in the SL buffers associated with the MAC entity. RRCcontrols BSR reporting for the sidelink by configuring the two timersperiodic-BSR-TimerSL and retx-BSR-TimerSL. Each sidelink logical channelbelongs to a ProSe Destination. Each sidelink logical channel isallocated to an LCG depending on the priority of the sidelink logicalchannel and the mapping between LCG ID and priority which is provided byupper layers in logicalChGroupInfoList. LCG is defined per ProSeDestination.

A sidelink Buffer Status Report (BSR) shall be triggered if any of thefollowing events occur: if the MAC entity has a configured SL-RNTI i) SLdata, for a sidelink logical channel of a ProSe Destination, becomesavailable for transmission in the RLC entity or in the PDCP entity andeither the data belongs to a sidelink logical channel with higherpriority than the priorities of the sidelink logical channels whichbelong to any LCG belonging to the same ProSe Destination and for whichdata is already available for transmission, or there is currently nodata available for transmission for any of the sidelink logical channelsbelonging to the same ProSe Destination, in which case the Sidelink BSRis referred below to as “Regular Sidelink BSR”, ii) UL resources areallocated and number of padding bits remaining after a Padding BSR hasbeen triggered is equal to or larger than the size of the Sidelink BSRMAC control element containing the buffer status for at least one LCG ofa ProSe Destination plus its subheader, in which case the Sidelink BSRis referred below to as “Padding Sidelink BSR”, iii) retx-BSR-TimerSLexpires and the MAC entity has data available for transmission for anyof the sidelink logical channels, in which case the Sidelink BSR isreferred below to as “Regular Sidelink BSR”, iv) periodic-BSR-TimerSLexpires, in which case the Sidelink BSR is referred below to as“Periodic Sidelink BSR”. Else, An SL-RNTI is configured by upper layersand SL data is available for transmission in the RLC entity or in thePDCP entity, in which case the Sidelink BSR is referred below to as“Regular Sidelink BSR”.

For Regular and Periodic Sidelink BSR, if the number of bits in the ULgrant is equal to or larger than the size of a Sidelink BSR containingbuffer status for all LCGs having data available for transmission plusits subheader, the MAC entity reports Sidelink BSR containing bufferstatus for all LCGs having data available for transmission. Else, theMAC entity reports Truncated Sidelink BSR containing buffer status foras many LCGs having data available for transmission as possible, takingthe number of bits in the UL grant into consideration.

If the Buffer Status reporting procedure determines that at least oneSidelink BSR has been triggered and not cancelled: if the MAC entity hasUL resources allocated for new transmission for this TTI and theallocated UL resources can accommodate a Sidelink BSR MAC controlelement plus its subheader as a result of logical channelprioritization, the MAC entity instructs the Multiplexing and Assemblyprocedure to generate the Sidelink BSR MAC control element(s), starts orrestarts periodic-BSR-TimerSL except when all the generated SidelinkBSRs are Truncated Sidelink BSRs, and starts or restartsretx-BSR-TimerSL.

Else if a Regular Sidelink BSR has been triggered, if an uplink grant isnot configured, a Scheduling Request shall be triggered.

A MAC PDU shall contain at most one Sidelink BSR MAC control element,even when multiple events trigger a Sidelink BSR by the time a SidelinkBSR can be transmitted in which case the Regular Sidelink BSR and thePeriodic Sidelink BSR shall have precedence over the padding SidelinkBSR.

The MAC entity shall restart retx-BSR-TimerSL upon reception of an SLgrant.

All triggered regular Sidelink BSRs shall be cancelled in case theremaining configured SL grant(s) valid for this SC Period canaccommodate all pending data available for transmission. All triggeredSidelink BSRs shall be cancelled in case the MAC entity has no dataavailable for transmission for any of the sidelink logical channels. Alltriggered Sidelink BSRs shall be cancelled when a Sidelink BSR (exceptfor Truncated Sidelink BSR) is included in a MAC PDU for transmission.All triggered Sidelink BSRs shall be cancelled, and retx-BSR-TimerSL andperiodic-BSR-TimerSL shall be stopped, when upper layers configureautonomous resource selection.

The MAC entity shall transmit at most one Regular/Periodic Sidelink BSRin a TTI. If the MAC entity is requested to transmit multiple MAC PDUsin a TTI, it may include a padding Sidelink BSR in any of the MAC PDUswhich do not contain a Regular/Periodic Sidelink BSR.

All Sidelink BSRs transmitted in a TTI always reflect the buffer statusafter all MAC PDUs have been built for this TTI. Each LCG shall reportat the most one buffer status value per TTI and this value shall bereported in all Sidelink BSRs reporting buffer status for this LCG

In Rel-13 ProSe, Per Packet Priority is defined for every packet, whichis used as the mechanism to perform prioritization for ProSeCommunication transmissions.

Currently, in MAC, SL BSR is triggered if SL data becomes available fortransmission for a ProSe Destination for which there is currently no SLdata available for transmission. This implies that SL BSR won't betriggered if there is data in any other LCGs of the same ProSeDestination. In this case, when SL data of higher PPPP becomes availablefor transmission, SL BSR won't be triggered and there would be delay inscheduling SL data of higher PPPP.

In order to cope with this problem, SL trigger condition can change sothat SL BSR is triggered per LCG I.e., SL BSR is triggered if SL databecomes available for transmission for a LCG for which there iscurrently no SL data available for transmission. In this case, when SLdata becomes available for transmission for empty LCG, SL BSR will betriggered regardless of SL data status in other LCGs of the same ProSeDestination. As a result, SL BSR may be triggered so frequently. As theeNB would schedule higher priority of SL data first, frequent SL BSRtrigger may not be so beneficial in terms of scheduling while itconsumes more UE battery power.

Therefore, a new mechanism is required to consider PPPP in SL BSRtrigger.

FIG. 13 is an example for sidelink configurations for triggering asidelink buffer status reporting in a D2D communication system accordingto embodiments of the present invention.

In this invention, for SL BSR trigger, when SL data of a sidelinklogical channel becomes available for transmission, the MAC entitychecks whether there is SL data available for transmission in any ofLCGs which have higher LCG priority and belong to the same ProSeDestination.

A UE is configured with at least one sidelink logical channel where, asidelink logical channel belongs to a ProSe Destination and the sidelinklogical channel belongs to an LCG of the ProSe Destination, wherein LCGis defined per ProSe Destination.

The sidelink logical channel is associated with a LCH priority, whereinthe LCH Priority refers the PPPP associated with that sidelink logicalchannel.

Let's take a following example in FIG. 13.

Let's assume that data is already available in LCH3. At this point oftime, if data becomes available in LCH2, it would be useful to triggerSL BSR to inform the eNB of arrival of higher priority data. However,there is no such trigger defined in current specification, and reportingof the higher priority data is delayed.

Therefore, we propose that even if there is already SL data avail fortransmission in a ProSe Destination, if a new data arrives at the higherpriority sidelink logical channel in the ProSe Destination, the UEtriggers SL BSR.

In this invention, the UE triggers SL BSR when a new data arrives at ahigher priority sidelink logical channel in a ProSe Destination thatalready has SL data.

When SL data becomes available for transmission for a sidelink logicalchannel of an LCG belonging to a ProSe Destination, within the sameProSe Destination, if there is no SL data available for transmission inany sidelink logical channel with LCH priority higher than or equal tothe LCH priority of this sidelink logical channel, the MAC entity shalltrigger SL BSR. Other word, within the same ProSe Destination, there isSL data available for transmission in a sidelink logical channel withLCH priority lower than the LCH priority of this sidelink logicalchannel, or there is SL data available for transmission in a sidelinklogical channel within different ProSe Destination, the MAC entity shalltrigger SL BSR.

Thus, according to the our invention, within the same ProSe Destination,there is SL data available for transmission in a sidelink logicalchannel with LCH priority higher than or equal to the LCH priority ofthis sidelink logical channel, the MAC entity shall not trigger SL BSR.

Text proposal for the our invention to 36.321 specification is shownbelow:

A sidelink Buffer Status Report (BSR) shall be triggered if any of thefollowing events occur:

if the MAC entity has a configured SL-RNTI:

SL data, for a sidelink logical channel of a ProSe Destination, becomesavailable for transmission in the RLC entity or in the PDCP entity andeither the SL data belongs to a sidelink logical channel with higherpriority than the priorities of the logical channels which belong to anyLCG in the same ProSe Destination and for which data is alreadyavailable for transmission, or there is currently no data available fortransmission for any of the sidelink logical channels belonging to thesame ProSe Destination, in which case the Sidelink BSR is referred belowto as “Regular Sidelink BSR”.

FIGS. 14 and 15 are diagrams for triggering a sidelink buffer statusreporting in a D2D communication system according to embodiments of thepresent invention.

The UE configures a plurality of ProSe destinations comprising a firstProSe destination including at least one first UE configured to receivedata from the UE and a second ProSe destination including at least onesecond UE configured to receive data from the UE, wherein the first andthe second ProSe destinations comprise one or more sidelink logicalchannels, respectively.

It is assumed that the second logical channel has a higher priority thana priority of the first sidelink logical channel, and the secondsidelink logical channel has a lower priority than a priority of a thirdsidelink logical channel (PPPP1 is the highest PPPP and PPPP3 is thelowest PPPP).

When a first sidelink logical channel already has a first sidelink data(S1401), if a second sidelink data for a second sidelink logical channelis received from the upper layer (S1405), the UE can trigger a bufferstatus reporting if the first sidelink logical channel and the secondsidelink logical channel belong to a same ProSe destination, while theUE has the first sidelink data for the first logical channel. In thiscase, even if the second sidelink logical channel has a lower prioritythan a priority of a third sidelink logical channel having a thirdsidelink data (S1403), the UE can also trigger the buffer statusreporting if the second sidelink logical channel and the third sidelinklogical channel belong to different ProSe destinations, respectively.

Preferably, the priority is a ProSe Per-Packet Priority.

In other word, in FIG. 15, when the UE configures a plurality of ProSedestinations comprising a first ProSe destination including at least onefirst UE and a second ProSe destination including at least one second UE(S1501), the UE configures a first sidelink logical channel and a secondsidelink logical channel belonging to the first ProSe destination, and athird sidelink logical channel belongs to the second ProSe destination(S1503). In this case, the third sidelink logical channel has a highestpriority and the first sidelink logical channel has a lowest priority,and a priority of the second sidelink logical channel is higher than thepriority of the first sidelink logical channel and lower than thepriority of the third sidelink logical channel.

The UE receives the first sidelink data for the third sidelink logicalchannel from an upper layer (S1505), and the second sidelink data forthe first sidelink logical channel from the upper layer (S1507).

When the third sidelink data arrives in the second sidelink logicalchannel from the upper layer (S1509), the UE can trigger a buffer statusreporting (S1511) even if the priority of the third logical channel isnot highest priority in a same MAC entity, only if the priority of thethird logical channel is highest priority in a same ProSe Destination.

If there are many sidelink logical channels configured for a ProSeDestination, the SL BSR may be frequently triggered with above ourinvention.

FIG. 16 is a diagram for triggering a sidelink buffer status reportingin a D2D communication system according to embodiments of the presentinvention.

Invention 2 is that within the same ProSe Destination, if there is no SLdata available for transmission in any sidelink logical channelbelonging to any LCG with LCG priority higher than or equal to the LCGpriority of this LCG

A LCG is associated with a LCG priority. The LCG Priority refers thehighest PPPP among the PPPPs of the sidelink logical channel belongingto the LCG

In Invention 2, the MAC entity shall trigger SL BSR, within the sameProSe Destination, there is SL data available for transmission in asidelink logical channel belonging to any LCG with LCG priority lowerthan the LCG priority of this LCG or there is SL data available fortransmission in a sidelink logical channel belonging to any LCG withindifferent ProSe Destination. Thus, within the same ProSe Destination,there is SL data available for transmission in a sidelink logicalchannel belonging to any LCG with LCG priority higher than or equal tothe LCG priority of this LCG the MAC entity shall not trigger SL BSR.

It means that the UE does not trigger SL BSR even if a new data arrivesat a higher priority logical channel if the LCG to which the higherpriority logical channel belongs has already SL data.

For example in FIG. 13, let's assume that data is already available inLCH2. At this point of time, if data becomes available in LCH1, the UEdoes not trigger SL BSR even if the LCH1 has higher priority becauseLCH1 and LCH2 belong to the same LCG

In the FIG. 16, an example is given for the invention 2.

It is assumed that LCG-PPPP mapping is [LCG1, PPPP1], [LCG2, PPPP2,PPPP3], [LCG3, PPPP4, PPPP5], [LCG4, PPPP6, PPPP7, PPPP8] wherein PPPP1is the highest PPPP and PPPP8 is the lowest PPPP.

According to the LCG-PPPP mapping, a LCG priority of each LCGs are: i)LCG1's LCG priority is PPPP1, ii) LCG2's LCG priority is PPPP2, iii)LCG3's LCG priority is PPPP4, iv) LCG4's LCG priority is PPPP6.

For ProSe Destination 1, the UE is configured with 4 sidelink logicalchannels, i.e., LCH1 with PPPP2, LCH2 with PPPP3, LCH3 with PPPP4, LCH4with PPPP7.

For ProSe Destination 2, the UE is configured with 2 sidelink logicalchannels, i.e., LCHS with PPPP3 and LCH6 with PPPP1.

First, there is no SL data available for transmission for ProSeDestination 1 and ProSe Destination 2.

SL data becomes available for transmission for LCH3 of ProSe Destination1 which belongs to LCG3. The MAC entity triggers SL BSR because there isno SL data available for transmission for any sidelink logical channelbelonging to this ProSe Destination 1 (S1601).

SL data becomes available for transmission for LCH6 of ProSe Destination2 which belongs to LCG1. The MAC entity triggers SL BSR because there isno SL data available for transmission for any sidelink logical channelbelonging to this ProSe Destination 2 (S 1603).

SL data becomes available for transmission for LCH2 of ProSe Destination1 which belongs to LCG2. The MAC entity triggers SL BSR because there isno SL data available for transmission for sidelink logical channelbelonging to any LCG with higher LCG priority than the LCG priority ofthis LCG2, i.e., PPPP2 in ProSe Destination 1 (S1605).

SL data becomes available for transmission for LCH4 of ProSe Destination1 which belongs to LCG4. The MAC entity doesn't trigger SL BSR becausethere is already SL data available for transmission for LCG2 and LCG3 ofProSe Destination 1 which have higher LCG priority, i.e., PPPP2 andPPPP4, than the LCG priority of LCG4, i.e., PPPP6, of ProSe Destination1 (S1607).

SL data becomes available for transmission for LCH1 of ProSe Destination1 which belongs to LCG 2. The MAC entity doesn't trigger SL BSR becausethere is already SL data available for transmission for sidelink logicalchannel belonging to this LCG2 (S1609).

SL data becomes available for transmission for LCHS of ProSe Destination2 which belongs to LCG2. The MAC entity doesn't trigger SL BSR becausethere is already SL data available for transmission for LCG1 of ProSeDestination 2 which has higher LCG priority, i.e., PPPP1, than the LCGpriority of LCG2, i.e., PPPP2, of ProSe Destination 2 (S1611).

Meanwhile, when SL data becomes available for transmission for asidelink logical channel of an LCG belonging to a ProSe Destination, theMAC entity can trigger SL BSR, within the MAC entity, if there is no SLdata available for transmission in any sidelink logical channelbelonging to any ProSe Destination with PD priority higher than or equalto the PD priority of this ProSe Destination (invention 3).

In Invention 3, the MAC entity shall trigger SL BSR, within the MACentity, there is SL data available for transmission in a sidelinklogical channel belonging to any ProSe Destination with PD prioritylower than the PD priority of this ProSe Destination. Other word, withinthe MAC entity, there is SL data available for transmission in asidelink logical channel belonging to any ProSe Destination with PDpriority higher than or equal to the PD priority of this ProSeDestination, the MAC entity shall not trigger SL BSR.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the scope of the present invention. The aboveembodiments are therefore to be construed in all aspects as illustrativeand not restrictive. The scope of the invention should be determined bythe appended claims, not by the above description, and all changescoming within the meaning of the appended claims are intended to beembraced therein.

1. A method for a user equipment (UE) operating in a wirelesscommunication system, the method comprising: configuring, by the UE, aplurality of Proximity based Services (ProSe) destinations, theconfiguring comprising: configuring a first ProSe destination includingat least one first UE configured to receive data from the UE; andconfiguring a second ProSe destination including at least one second UEconfigured to receive the data from the UE, wherein the first and thesecond ProSe destinations comprise one or more sidelink logicalchannels, respectively, receiving, by the UE from an upper layer, firstsidelink data for a first sidelink logical channel of a given ProSedestination, the first sidelink logical channel having the highestpriority among priorities of sidelink logical channels belonging to thegiven ProSe destination and for which data is already available;receiving, by the UE from the upper layer, second sidelink data for asecond sidelink logical channel, wherein the second logical channel hasa priority higher than the priority of the first sidelink logicalchannel while the first sidelink data is available for transmission viathe first logical channel; and if the first sidelink logical channel andthe second sidelink logical channel belong to a same ProSe destination,triggering a buffer status reporting process when the second sidelinkdata is received.
 2. The method according to claim 1, furthercomprising: even if the second sidelink logical channel has a prioritylower than a priority of a third sidelink logical channel having thirdsidelink data, the buffer status reporting process is triggered by theUE if the second sidelink logical channel and the third sidelink logicalchannel belong to different ProSe destinations, respectively.
 3. Themethod according to claim 1, wherein the priority is a ProSe Per-PacketPriority.
 4. A method for a user equipment (UE) operating in a wirelesscommunication system, the method comprising: configuring, by the UE, aplurality of Proximity based Services (ProSe) destinations, theconfiguring comprising: configuring a first ProSe destination includingat least one first UE configured to receive data from the UE; andconfiguring a second ProSe destination including at least one second UEconfigured to receive data from the UE, configuring a first sidelinklogical channel and a second sidelink logical channel belonging to thefirst ProSe destination, and a third sidelink logical channel belongingto the second ProSe destination, wherein the third sidelink logicalchannel has a highest priority among the priorities of all the sidelinklogical channels configured for the UE and the first sidelink logicalchannel has a lowest priority among the first, second and third sidelinklogical channels, and a priority of the second sidelink logical channelis higher than the priority of the first sidelink logical channel andlower than the priority of the third sidelink logical channel;receiving, by the UE from an upper layer, first sidelink data for thethird sidelink logical channel; receiving, by the UE from the upperlayer, second sidelink data for the first sidelink logical channel,wherein the first sidelink logical channel having the highest priorityamong priorities of sidelink logical channels belonging to the firstProSe destination and for which data is already available; and if the UEholds the first sidelink data for the third logical channel and thesecond sidelink data for the first sidelink logical channel when thirdsidelink data arrives in the second sidelink logical channel from theupper layer, triggering a buffer status reporting process.
 5. The methodaccording to claim 4, wherein first sidelink logical channel, the secondsidelink logical channel, and the third sidelink logical channel belongto a same Medium Access Control (MAC) entity.
 6. The method according toclaim 4, wherein the priority is a ProSe Per-Packet Priority.
 7. A UserEquipment (UE) for operating in a wireless communication system, the UEcomprising: a Radio Frequency (RF) module; and a processor operablycoupled with the RF module and configured to: configure a plurality ofProximity based Services (ProSe) destinations by: configuring a firstProSe destination including at least one first UE configured to receivedata from the UE; and configuring a second ProSe destination includingat least one second UE configured to receive the data from the UE,wherein the first and the second ProSe destinations comprise one or moresidelink logical channels, respectively, receive, from an upper layer,first sidelink data for a first sidelink logical channel of a givenProSe destination, the first sidelink logical channel having the highestpriority among priorities of sidelink logical channels belonging to thegiven ProSe destination and for which data is already available;receive, from the upper layer, second sidelink data for a secondsidelink logical channel, wherein the second logical channel has apriority higher than the priority of the first sidelink logical channel,while the first sidelink data is available for transmission via thefirst logical channel; and if the first sidelink logical channel and thesecond sidelink logical channel belong to a same ProSe destination,trigger a buffer status reporting process when the second sidelink datais received.
 8. The UE according to claim 7, wherein, even if the secondsidelink logical channel has a priority lower than a priority of a thirdsidelink logical channel having third sidelink data, the UE triggers thebuffer status reporting process if the second sidelink logical channeland the third sidelink logical channel belong to different ProSedestinations, respectively.
 9. The UE according to claim 7, wherein thepriority is a ProSe Per-Packet Priority.
 10. A User Equipment (UE) foroperating in a wireless communication system, the UE comprising: a RadioFrequency (RF) module; and a processor operably coupled with the RFmodule and configured to: configure a plurality of Proximity basedServices (ProSe) destinations by: configuring a first ProSe destinationincluding at least one first UE configured to receive data from the UE;and configuring a second ProSe destination including at least one secondUE configured to receive data from the UE, configure a first sidelinklogical channel and a second sidelink logical channel belonging to thefirst ProSe destination, and a third sidelink logical channel belongingto the second ProSe destination; wherein the third sidelink logicalchannel has a highest priority among the priorities of all the sidelinklogical channels configured for the UE and the first sidelink logicalchannel has a lowest priority among the first, second and third sidelinklogical channels, and a priority of the second sidelink logical channelis higher than the priority of the first sidelink logical channel andlower than the priority of the third sidelink logical channel; receivefirst sidelink data for the third sidelink logical channel from an upperlayer; receive second sidelink data for the first sidelink logicalchannel from the upper layer, wherein the first sidelink logical channelhaving the highest priority among priorities of sidelink logicalchannels belonging to the first ProSe destination and for which data isalready available; and if the UE holds the first sidelink data for thethird logical channel and the second sidelink data for the firstsidelink logical channel when third sidelink data arrives in the secondsidelink logical channel from the upper layer, trigger a buffer statusreporting process.
 11. The UE according to claim 10, wherein firstsidelink logical channel, the second sidelink logical channel, and thethird sidelink logical channel belong to a same Medium Access Control(MAC) entity.
 12. The UE according to claim 10, wherein the priority isa ProSe Per-Packet Priority.
 13. The method of claim 1, furthercomprising: transmitting the first sidelink data via the first sidelinklogical channel upon receiving a corresponding sidelink grant.
 14. Themethod of claim 1, further comprising: transmitting the second sidelinkdata via the second sidelink logical channel upon receiving acorresponding sidelink grant.
 15. The UE according to claim 7, whereinthe processor is further configured to transmit the first sidelink datavia the first sidelink logical channel upon receiving a correspondingsidelink grant.
 16. The UE according to claim 7, wherein the processoris further configured to transmit the second sidelink data via thesecond sidelink logical channel upon receiving a corresponding sidelinkgrant.
 17. The method of claim 4, further comprising: transmitting thefirst sidelink data via the third sidelink logical channel uponreceiving a corresponding sidelink grant.
 18. The method of claim 4,further comprising: transmitting the second sidelink data via the firstsidelink logical channel upon receiving a corresponding sidelink grant.19. The UE according to claim 10, wherein the processor is furtherconfigured to transmit the first sidelink data via the third sidelinklogical channel upon receiving a corresponding sidelink grant.
 20. TheUE according to claim 10, wherein the processor is further configured totransmit the second sidelink data via the first sidelink logical channelupon receiving a corresponding sidelink grant.